Electrical transmission system

ABSTRACT

The electrical transmission system for a motor vehicle having a traction input, a power electronic system that controls the traction input and a cooling system for cooling the power electronic system. The cooling system is a refrigerator, or possibly a heat pump, with an integrated carburetor and a compressor unit. The electrical transmission system is particularly suitable for urban buses.

[0001] According to the preamble of claim 1, this invention concerns an electrical transmission system for motor vehicles, specially urban buses, having a traction input and a power electronic system that controls it.

[0002] Electrical transmission system known already, specially for urban buses, have a traction input in the form of an electromotor which is often designed as asynchronous machine, that is, having a stator and a rotor provided in the stator. The rotor is usually designed as squirrel cage motor and consists of electrically conductive aluminum which in the form of a pressure casting can be shaped as a rotor. During production the aluminum is preferably poured in the grooves formed by the laminated bundle of the rotor wherein on the front side of the rotor aluminum rods from the respective grooves are interlocked and thus short circuited. Such asynchronous motors are chiefly highly utilized motors whose heat development needs an optimized cooling.

[0003] EP 0 484,548 has disclosed such as electrical machine with an internal rotor with rotor shaft and with a rotor laminated bundle with external stator. Said electrical machine is connected with the coolant circuit of the vehicle.

[0004] However, the transportation of coolant in such an electrical machine is made difficult by the structurally determined spatial limitation whereby the collected heat amounts can be removed only with difficulty, specially in highly used machines.

[0005] In the Applicant's German Patent Application No. 199 055 38 an electromotor was proposed for driving vehicles which has an external stator, an internal pivotally mounted rotor, a rotor laminated bundle and a rotor shaft non-turnably connected with the rotor laminated bundle, the rotor being designed hollow and the rotor shaft as spider shaft. The spider shaft has on its periphery a number of webs which, to form small heat-transfer surfaces, abut only on almost linear contact surface on the rotor laminated bundle. The webs are designed so as to have the needed strength and rigidity but a small surface contact with the heat-generating laminated bundle.

[0006] It is thus possible to protect the support of the rotor shaft and the seals thereof against damages resulting from the high amounts of heat transferred to the bearings.

[0007] The Applicant's German Patent Application No. 199 055 39 has disclosed one other electromotor for driving vehicles in which a gear exchanger for cooling a coolant used in the electromotor is integrated in the electromotor wherein the coolant can be passed in the ducts having large cross-sections and wherein the heat exchanger can be placed in one of said ducts. The heat exchanger can here be provided with cooling tubes which surround the stator, it being possible for the cooling tubes in the heat exchanger to be connected with cooling webs for heat transfer.

[0008] The Applicant's German Patent Application No. 199 055 40 finally describes an electromotor for driving vehicles having an external stator and an internal pivotally mounted rotor with a laminated bundle wand with a rotor shaft non-turnably connected with the rotor laminated bundle, the rotor being designed hollow and in the area between rotor laminated bundle and rotor shaft, a coolant is passed through. The rotor shaft can be designed in the shape of a worm conveyor or be provided with vent devices on an least one of its axial ends for enlarging the flow rate or the feed pressure of the coolant. Thereby is made possible an improved transportation of the coolant so that the support of the machine be protected from damages.

[0009] However, together with said different parts of the electromotor, the power electronics of such traction inputs must be cooled. The degree of effectiveness of the parts used therein depends on the operating temperature. With adequately low coolant temperature it is possible to change over to a correspondingly high power. In case of automotive utilizations, it is then possible with the conventional hot air exchangers no longer to cool the initial temperature to below 50° C. when the cool air already has a temperature of 40° C.

[0010] The problem to be solved by this invention is to provide an effective cooling system for the power electronics of traction inputs.

[0011] Based on an electrical transmission system for motor vehicles and specially urban buses of the kind specifically mentioned above, this problem i solved by the feature stated in the characteristic part of claim 1; advantageous developments are described in the sub-claims.

[0012] Therefore, it is provided according to the invention that the cooling system for the power electronics consists of a refrigerator or heat pump with integrated carburetor and compressor unit. The coolant can thus be brought to adequately low temperature according to the lay out.

[0013] The coolant of the refrigerator or heat pump can be used directly for cooling the corresponding parts of the power electronics; the coolant can also be used to cool the parts indirectly via a secondary circuit.

[0014] In vehicles having built-in air conditioning equipment, the latter can be switched on as additional cooling system via an adequate terminal.

[0015] The inventive installation of a refrigerator or heat pump reduces the temperature of the parts thus leading to increased effectiveness. A reduction in weight and installation space of the traditional coolers is at the same time made possible. When a heat pum is used, the reverse temperature can be set adequately high so as to have a great difference from the temperature of the cool air. With a temperature difference adequately great, the specific cooling capacity is in creased and a slimmer cooling surface design is made possible.

[0016] By adequate selection of the coolant and of the pressure level of the heat pump or refrigerator, the reverse cooling to high temperature level is also possible so that the connection can also be implemented on existing cooling units such as fuel cell cooling, internal combustion engine cooling, air conditioning systems, etc.

[0017] The existing air conditioning in the vehicle can even be used as heat pump for direct or indirect cooling.

[0018] With multiple use of the existing units a reduction of the total weight can be obtained. A reduction fo the number of parts at the same time allows in turn a higher reliability of the whole system.

[0019] According to the invention, by heat pump is understood in the conventional sense an arrangement where in a cycle process with the aid of supplied work a temperature difference is created wherein heat from a heat accumulator of lower temperature is pumped into one with higher temperature. Conversely, in a traditional refrigerator according to the 2^(nd) law of thermodynamics, the reduction fo he entropy of the system related to the product of a temperature difference is compensated by supplying labor or heat. 

1. Electrical transmission system for motor vehicles, specially urban buses, having a traction input, a power electronic system that controls it and a cooling system for the power electronic system, characterized in that the cooling system is a refrigerator with integrated carburetor and compressor unit.
 2. Transmission system according to claim 1, characterized in that said refrigerator is connected via a primary circuit with the parts to be cooled of the power electronic system.
 3. Transmission system according to claim 1, characterized in that said refrigerator is connected via a secondary circuit with the parts to be cooled of the power electronic system.
 4. Transmission system according to any one of the preceding claims, characterized in that the cooling system is provided with a terminal for connection with an air-conditioning equipment in the motor vehicle.
 5. Transmission system according to any one of the preceding claims, characterized in that said refrigerator is provided with a terminal for connection with a fuel cell cooling existing in the motor vehicle.
 6. Transmission system according to any one of the preceding claims, characterized in that the cooling system is provided with a terminal for connection with the internal combustion engine cooling existing in the motor vehicle. 